Methods and devices for lighting displays

ABSTRACT

Various devices and methods of lighting a display are disclosed. In one embodiment, for example, a display device includes a transmissive display configured to be illuminated through a back surface and a reflective display configured to be illuminated through a front surface. A light source is disposed with respect to the back of the transmissive display to illuminate the transmissive display through the back surface. A light pipe is disposed with respect to the light source to receive light from the light source and is configured to propagate the light such that this light provides front illumination of the reflective display.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.11/187,784 titled METHODS AND DEVICES FOR LIGHTING DISPLAYS, filed Jul.22, 2005, which claims priority to U.S. Provisional Application No.60/613,264 titled METHOD AND DEVICE FOR LIGHTING A DISPLAY, filed Sep.27, 2004, each of which is incorporated by reference in its entirety.

BACKGROUND

1. Field of the Invention

The field of the invention relates to microelectromechanical systems(MEMS).

2. Description of the Related Technology

Microelectromechanical systems (MEMS) include micro mechanical elements,actuators, and electronics. Micromechanical elements may be createdusing deposition, etching, and or other micromachining processes thatetch away parts of substrates and/or deposited material layers or thatadd layers to form electrical and electromechanical devices. One type ofMEMS device is called an interferometric modulator. As used herein, theterm interferometric modulator or interferometric light modulator refersto a device that selectively absorbs and/or reflects light using theprinciples of optical interference. In certain embodiments, aninterferometric modulator may comprise a pair of conductive plates, oneor both of which may be transparent and/or reflective in whole or partand capable of relative motion upon application of an appropriateelectrical signal. In a particular embodiment, one plate may comprise astationary layer deposited on a substrate and the other plate maycomprise a metallic membrane separated from the stationary layer by anair gap. As described herein in more detail, the position of one platein relation to another can change the optical interference of lightincident on the interferometric modulator. Such devices have a widerange of applications, and it would be beneficial in the art to utilizeand/or modify the characteristics of these types of devices so thattheir features can be exploited in improving existing products andcreating new products that have not yet been developed.

SUMMARY OF CERTAIN EMBODIMENTS

The system, method, and devices of the invention each have severalaspects, no single one of which is solely responsible for its desirableattributes. Without limiting the scope of this invention, its moreprominent features will now be discussed briefly. After considering thisdiscussion, and particularly after reading the section entitled“Detailed Description of Certain Embodiments” one will understand howthe features of this invention provide advantages over other displaydevices.

The invention includes display systems and methods of illuminating adisplay. One embodiment includes a display device that includes atransmissive display including a front surface and a back surface, thetransmissive display configured to be illuminated through the backsurface, a reflective display comprising a front surface and a backsurface, said reflective display configured to be illuminated throughthe front surface, a light source disposed with respect to the back ofthe transmissive display to illuminate the transmissive display throughthe back surface, and a light pipe disposed with respect to the lightsource to receive light therefrom, said light pipe configured topropagate said light such that said light provides front illumination ofsaid reflective display.

Another embodiment includes a method of illuminating a reflectivedisplay and a transmissive display with a light source, the reflectiveand transmissive displays being positioned in a back-to-backconfiguration, the method including disposing the light source withrespect to a back portion of the transmissive display to illuminate thetransmissive display through the back, disposing a light pipe withrespect to the light source to receive light therefrom, and disposingthe reflective display with respect to the light pipe such that lightexiting the light pipe provides front illumination for the reflectivedisplay. Yet another embodiment includes a display device manufacturedby such a method of illuminating a reflective display and a transmissivedisplay with a light source.

Another embodiment includes a display device, includes a firstreflective display including a viewable surface and a back surface, asecond reflective display including a viewable surface and a backsurface, the back surface of the first display disposed substantiallyfacing the back surface of the second display and positioned near theback surface of the second display, a light source, and light pipingcoupled to the light source and coupled to an edge or surface of boththe first and second displays to transfer light emitted from the lightsource into a portion of the viewable surface of both the first andsecond displays illuminating the first and second displays.

Another embodiment includes a microelectromechanical systems (MEMS)display device, including first means for displaying an image, the firstmeans for displaying comprising a front surface and a back surface,means for illuminating the first means for displaying through the backsurface, second means for displaying an image comprising a front surfaceand a back surface, and means for illuminating the second means fordisplaying through the front surface of the second means for displaying,wherein the means for illuminating the second means for displaying useslight from the means for illuminating teh first means for displaying.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an isometric view depicting a portion of one embodiment of aninterferometric modulator display in which a movable reflective layer ofa first interferometric modulator is in a relaxed position and a movablereflective layer of a second interferometric modulator is in an actuatedposition.

FIG. 2 is a system block diagram illustrating one embodiment of anelectronic device incorporating a 3x3 interferometric modulator display.

FIG. 3 is a diagram of movable mirror position versus applied voltagefor one exemplary embodiment of an interferometric modulator of FIG. 1.

FIG. 4 is an illustration of a set of row and column voltages that maybe used to drive an interferometric modulator display.

FIG. 5A illustrates one exemplary frame of display data in the 3×3interferometric modulator display of FIG. 2.

FIG. 5B illustrates one exemplary timing diagram for row and columnsignals that may be used to write the frame of FIG. 5A.

FIGS. 6A and 6B are system block diagrams illustrating an embodiment ofa visual display device comprising a plurality of interferometricmodulators.

FIG. 7A is a cross section of the device of FIG. 1.

FIG. 7B is a cross section of an alternative embodiment of aninterferometric modulator.

FIG. 7C is a cross section of another alternative embodiment of aninterferometric modulator.

FIG. 7D is a cross section of yet another alternative embodiment of aninterferometric modulator.

FIG. 7E is a cross section of an additional alternative embodiment of aninterferometric modulator.

FIG. 8 is a diagram schematically illustrating a mobile phone with aclamshell-like structure that includes a sub-display disposed on anexterior surface of the clamshell.

FIG. 9 is a diagram schematically illustrating a mobile phone with aclamshell-like structure that includes a principle display disposed onan interior surface of the clamshell.

FIG. 10 is a diagram schematically illustrating a cross section of abacklight disposed between a principle display and a sub-display.

FIG. 11 is a diagram schematically illustrating light exit regions on asurface of a backlight.

FIG. 12 is a cross section schematically illustrating a display devicethat includes a backlight configured to illuminate a reflectivesub-display and a principle display that is transmissive.

FIG. 13A schematically depicts a front view of an embodiment of adisplay device that includes a sub-display illuminated by a backlightthrough an annular light pipe that provides light to all sides of thesub-display.

FIG. 13B schematically depicts a perspective view of the annular lightpipe, backlight, and sub-display of FIG. 13A.

FIG. 13C schematically depicts a perspective view of the annular lightpipe of FIG. 13A.

FIG. 14 is a cross sectional view schematically illustrating anembodiment of a display device having a backlight that illuminates areflective display using a light pipe.

FIG. 15 is a cross sectional view schematically illustrating anembodiment of a display device that includes a backlight that providesillumination to a sub-display via a backplate configured as a lightpipe.

FIG. 16 is a cross sectional view schematically illustrating anembodiment of a display device that includes a backlight that providesillumination to a sub-display via a backplate configured as a light pipeand optical coupling material.

FIG. 17 is a cross sectional view schematically illustrating anembodiment of a display device that includes a substantially opticallytransmissive component disposed forward of a reflective display.

FIG. 18 is a cross sectional view schematically illustrating anembodiment of a display device illuminated by light spilled on a frontsurface of the display.

FIG. 19 is a cross sectional view schematically illustrating anembodiment of a display device illuminated by light distributed in acontrolled manner on a front surface of the display.

FIG. 20 is a cross sectional view schematically illustrating anembodiment of a display device having first and second backplates thatchannel light to first and second reflective displays, respectively.

FIG. 21 schematically depicts an example of a spatial light modulatorhaving scatter features or illumination dots.

FIG. 22 schematically depicts an embodiment of an illumination dotpattern used with a backlight.

FIG. 23 schematically depicts embodiments of possible positions for thearray of illumination dots.

FIG. 24 is a flow chart showing different methods for manufacturing aspatial light modulator with illumination dots.

DETAILED DESCRIPTION OF CERTAIN EMBODIMENTS

The following detailed description is directed to certain specificembodiments of the invention. However, the invention can be embodied ina multitude of different ways. In this description, reference is made tothe drawings wherein like parts are designated with like numeralsthroughout. As will be apparent from the following description, theembodiments may be implemented in any device that is configured todisplay an image, whether in motion (e.g., video) or stationary (e.g.,still image), and whether textual or pictorial. More particularly, it iscontemplated that the embodiments may be implemented in or associatedwith a variety of electronic devices such as, but not limited to, mobiletelephones, wireless devices, personal data assistants (PDAs), hand-heldor portable computers, GPS receivers/navigators, cameras, MP3 players,camcorders, game consoles, wrist watches, clocks, calculators,television monitors, flat panel displays, computer monitors, autodisplays (e.g., odometer display, etc.), cockpit controls and/ordisplays, display of camera views (e.g., display of a rear view camerain a vehicle), electronic photographs, electronic billboards or signs,projectors, architectural structures, packaging, and aestheticstructures (e.g., display of images on a piece of jewelry). MEMS devicesof similar structure to those described herein can also be used innon-display applications such as in electronic switching devices.

Various embodiments described herein include devices and methods oflighting a display using a light source and light pipes. In oneembodiment, for example, a display includes a transmissive displayconfigured to be illuminated through a back surface and a reflectivedisplay configured to be illuminated through a front surface. Thedisplay includes a single light source sandwiched between thetransmissive display and the reflective display. The light sourceilluminates the transmissive display through its back surface. A lightpipe receives light from the light source and propagates the light sothat it illuminates the reflective display through a front surface oredge of the display. Various embodiments of the light pipe and the lightsource are possible depending on the application of the display.

A cellular phone is an example of a product in which the MEMS device canbe used in a display. Cellular phones featuring a “clamshell-like”structure are typically closed when not in use and then opened toreceive a telephone call. Such cellular phones do not allow viewing of aprinciple display located on an interior surface of the clamshell whenthe phone is closed. Consequently, a second smaller, less sophisticateddisplay, which is sometimes referred to herein as a “sub-display,” canbe included on an outer surface of the clamshell that is visible whenthe phone is closed to provide “quick-look” information withoutrequiring a user to open the phone. The principle display andsub-display can be transmissive or transflective LCDs, which usebackside illumination. To lower the cost and complexity of the cellularphone and to keep the clamshell as thin as possible, a single backlightplaced in-between the principle display and sub-display can be used toilluminate both displays. In one embodiment, the backlight illuminatesthe principle display through a rear surface of the principle display.The backlight is configured with one or more light-leaking regions onits rear surface that correspond to the area of the sub-display. Lightcontrol patterns, for example, patterns on films attached to thebacklight or patterns disposed directly on the backlight itself, can beused so that uniformity of light emitted from the front surface of thebacklight is not disturbed by the loss of light that leaks out the rearsurface to the sub-display.

When the transmissive or transflective sub-display is replaced by areflective display, e.g., an interferometric modulator (MEMS device),that utilizes frontside illumination, it is more difficult to share thebacklight because light exiting the rear surface of the backlight lightwill hit the opaque back side of the reflective display and provide nouseful illumination. One solution is to equip the reflective displaywith a frontlight. This solution works, but it has several undesirableconsequences. First, the extra light adds cost and complexity to theproduct. Second, a front light increases the thickness of the displayand the cell phone incorporating the display, and hence decreases themarket desirability of the product.

Methods and systems are described herein include illuminating reflectivedisplays using a single backlight to reduce the size and cost associatedwith adding an additional front light. Light from the backlight can bechanneled with a light pipe to a portion of the reflective display, suchas an edge of the display or the front of the display. For example, in adual display clamshell cellular phone, a backlight provides rearillumination of a transmissive display located on one face of theclamshell, or portion thereof, and simultaneously provides frontillumination of a reflective display, such as an interferometricmodulator display, located on the opposite face of the clamshell,through light pipe structures. Light pipes may be at least partiallyincorporated into the backplate of the reflective display, in someembodiments. In certain embodiments, a single light source with one ormore light pipes can be used to illuminate reflective displays on bothfaces of the device.

One interferometric modulator display embodiment comprising aninterferometric MEMS display element is illustrated in FIG. 1. In thesedevices, the pixels are in either a bright or dark state. In the bright(“on” or “open”) state, the display element reflects a large portion ofincident visible light to a user. When in the dark (“off” or “closed”)state, the display element reflects little incident visible light to theuser. Depending on the embodiment, the light reflectance properties ofthe “on” and “off” states may be reversed. MEMS pixels can be configuredto reflect predominantly at selected colors, allowing for a colordisplay in addition to black and white.

FIG. 1 is an isometric view depicting two adjacent pixels in a series ofpixels of a visual display, wherein each pixel comprises a MEMSinterferometric modulator. In some embodiments, an interferometricmodulator display comprises a row/column array of these interferometricmodulators. Each interferometric modulator includes a pair of reflectivelayers positioned at a variable and controllable distance from eachother to form a resonant optical cavity with at least one variabledimension. In one embodiment, one of the reflective layers may be movedbetween two positions. In the first position, referred to herein as therelaxed position, the movable reflective layer is positioned at arelatively large distance from a fixed partially reflective layer. Inthe second position, referred to herein as the actuated position, themovable reflective layer is positioned more closely adjacent to thepartially reflective layer. Incident light that reflects from the twolayers interferes constructively or destructively depending on theposition of the movable reflective layer, producing either an overallreflective or non-reflective state for each pixel.

The depicted portion of the pixel array in FIG. 1 includes two adjacentinterferometric modulators 12 a and 12 b. In the interferometricmodulator 12 a on the left, a movable reflective layer 14 a isillustrated in a relaxed position at a predetermined distance from anoptical stack 16 a, which includes a partially reflective layer. In theinterferometric modulator 12 b on the right, the movable reflectivelayer 14 b is illustrated in an actuated position adjacent to theoptical stack 16 b.

The optical stacks 16 a and 16 b (collectively referred to as opticalstack 16), as referenced herein, typically comprise of several fusedlayers, which can include an electrode layer, such as indium tin oxide(ITO), a partially reflective layer, such as chromium, and a transparentdielectric. The optical stack 16 is thus electrically conductive,partially transparent and partially reflective, and may be fabricated,for example, by depositing one or more of the above layers onto atransparent substrate 20. In some embodiments, the layers are patternedinto parallel strips, and may form row electrodes in a display device asdescribed further below. The movable reflective layers 14 a, 14 b may beformed as a series of parallel strips of a deposited metal layer orlayers (orthogonal to the row electrodes of 16 a, 16 b) deposited on topof posts 18 and an intervening sacrificial material deposited betweenthe posts 18. When the sacrificial material is etched away, the movablereflective layers 14 a, 14 b are separated from the optical stacks 16 a,16 b by a defined gap 19. A highly conductive and reflective materialsuch as aluminum may be used for the reflective layers 14, and thesestrips may form column electrodes in a display device.

With no applied voltage, the cavity 19 remains between the movablereflective layer 14 a and optical stack 16 a, with the movablereflective layer 14 a in a mechanically relaxed state, as illustrated bythe pixel 12 a in FIG. 1. However, when a potential difference isapplied to a selected row and column, the capacitor formed at theintersection of the row and column electrodes at the corresponding pixelbecomes charged, and electrostatic forces pull the electrodes together.If the voltage is high enough, the movable reflective layer 14 isdeformed and is forced against the optical stack 16. A dielectric layer(not illustrated in. this Figure) within the optical stack 16 mayprevent shorting and control the separation distance between layers 14and 16, as illustrated by pixel 12 b on the right in FIG. 1. Thebehavior is the same regardless of the polarity of the applied potentialdifference. In this way, row/column actuation that can control thereflective vs. non-reflective pixel states is analogous in many ways tothat used in conventional LCD and other display technologies.

FIGS. 2 through 5B illustrate one exemplary process and system for usingan array of interferometric modulators in a display application.

FIG. 2 is a system block diagram illustrating one embodiment of anelectronic device that may incorporate aspects of the invention. In theexemplary embodiment, the electronic device includes a processor 21which may be any general purpose single- or multi-chip microprocessorsuch as an ARM, Pentium®, Pentium II®, Pentium III®, Pentium IV®,Pentium® Pro, an 8051, a MIPS , a Power PC®, an ALPHA®, or any specialpurpose microprocessor such as a digital signal processor,microcontroller, or a programmable gate array. As is conventional in theart, the processor 21 may be configured to execute one or more softwaremodules. In addition to executing an operating system, the processor maybe configured to execute one or more software applications, including aweb browser, a telephone application, an email program, or any othersoftware application.

In one embodiment, the processor 21 is also configured to communicatewith an array driver 22. In one embodiment, the array driver 22 includesa row driver circuit 24 and a column driver circuit 26 that providesignals to a panel or display array (display) 30. The cross section ofthe array illustrated in FIG. 1 is shown by the lines 1-1 in FIG. 2. ForMEMS interferometric modulators, the row/column actuation protocol maytake advantage of a hysteresis property of these devices illustrated inFIG. 3. It may require, for example, a 10 volt potential difference tocause a movable layer to deform from the relaxed state to the actuatedstate. However, when the voltage is reduced from that value, the movablelayer maintains its state as the voltage drops back below 10 volts. Inthe exemplary embodiment of FIG. 3, the movable layer does not relaxcompletely until the voltage drops below 2 volts. There is thus a rangeof voltage, about 3 to 7 V in the example illustrated in FIG. 3, wherethere exists a window of applied voltage within which the device isstable in either the relaxed or actuated state. This is referred toherein as the “hysteresis window” or “stability window.” For a displayarray having the hysteresis characteristics of FIG. 3, the row/columnactuation protocol can be designed such that during row strobing, pixelsin the strobed row that are to be actuated are exposed to a voltagedifference of about 10 volts, and pixels that are to be relaxed areexposed to a voltage difference of close to zero volts. After thestrobe, the pixels are exposed to a steady state voltage difference ofabout 5 volts such that they remain in whatever state the row strobe putthem in. After being written, each pixel sees a potential differencewithin the “stability window” of 3-7 volts in this example. This featuremakes the pixel design illustrated in FIG. 1 stable under the sameapplied voltage conditions in either an actuated or relaxed pre-existingstate. Since each pixel of the interferometric modulator, whether in theactuated or relaxed state, is essentially a capacitor formed by thefixed and moving reflective layers, this stable state can be held at avoltage within the hysteresis window with almost no power dissipation.Essentially no current flows into the pixel if the applied potential isfixed.

In typical applications, a display frame may be created by asserting theset of column electrodes in accordance with the desired set of actuatedpixels in the first row. A row pulse is then applied to the row 1electrode, actuating the pixels corresponding to the asserted columnlines. The asserted set of column electrodes is then changed tocorrespond to the desired set of actuated pixels in the second row. Apulse is then applied to the row 2 electrode, actuating the appropriatepixels in row 2 in accordance with the asserted column electrodes. Therow 1 pixels are unaffected by the row 2 pulse, and remain in the statethey were set to during the row 1 pulse. This may be repeated for theentire series of rows in a sequential fashion to produce the frame.Generally, the frames are refreshed and/or updated with new display databy continually repeating this process at some desired number of framesper second. A wide variety of protocols for driving row and columnelectrodes of pixel arrays to produce display frames are also well knownand may be used in conjunction with the present invention.

FIGS. 4, 5A and 5B illustrate one possible actuation protocol forcreating a display frame on the 3×3 array of FIG. 2. FIG. 4 illustratesa possible set of column and row voltage levels that may be used forpixels exhibiting the hysteresis curves of FIG. 3. In the FIG. 4embodiment, actuating a pixel involves setting the appropriate column to−V_(bias), and the appropriate row to +ΔV, which may correspond to −5volts and +5 volts respectively Relaxing the pixel is accomplished bysetting the appropriate column to +V_(bias), and the appropriate row tothe same +ΔV, producing a zero volt potential difference across thepixel. In those rows where the row voltage is held at zero volts, thepixels are stable in whatever state they were originally in, regardlessof whether the column is at +V_(bias), or −V_(bias). As is alsoillustrated in FIG. 4, it will be appreciated that voltages of oppositepolarity than those described above can be used, e.g., actuating a pixelcan involve setting the appropriate column to +V_(bias), and theappropriate row to −ΔV. In this embodiment, releasing the pixel isaccomplished by setting the appropriate column to −V_(bias), and theappropriate row to the same −ΔV, producing a zero volt potentialdifference across the pixel.

FIG. 5B is a timing diagram showing a series of row and column signalsapplied to the 3×3 array of FIG. 2 which will result in the displayarrangement illustrated in FIG. 5A, where actuated pixels arenon-reflective. Prior to writing the frame illustrated in FIG. 5A, thepixels can be in any state, and in this example, all the rows are at 0volts, and all the columns are at +5 volts. With these applied voltages,all pixels are stable in their existing actuated or relaxed states.

In the FIG. 5A frame, pixels (1,1), (1,2), (2,2), (3,2) and (3,3) areactuated. To accomplish this, during a “line time” for row 1, columns 1and 2 are set to −5 volts, and column 3 is set to +5 volts. This doesnot change the state of any pixels, because all the pixels remain in the3-7 volt stability window. Row 1 is then strobed with a pulse that goesfrom 0, up to 5 volts, and back to zero. This actuates the (1,1) and(1,2) pixels and relaxes the (1,3) pixel. No other pixels in the arrayare affected. To set row 2 as desired, column 2 is set to −5 volts, andcolumns 1 and 3 are set to +5 volts. The same strobe applied to row 2will then actuate pixel (2,2) and relax pixels (2,1) and (2,3). Again,no other pixels of the array are affected. Row 3 is similarly set bysetting columns 2 and 3 to -5 volts, and column 1 to +5 volts. The row 3strobe sets the row 3 pixels as shown in FIG. 5A. After writing theframe, the row potentials are zero, and the column potentials can remainat either +5 or −5 volts, and the display is then stable in thearrangement of FIG. 5A. It will be appreciated that the same procedurecan be employed for arrays of dozens or hundreds of rows and columns. Itwill also be appreciated that the timing, sequence, and levels ofvoltages used to perform row and column actuation can be varied widelywithin the general principles outlined above, and the above example isexemplary only, and any actuation voltage method can be used with thesystems and methods described herein.

FIGS. 6A and 6B are system block diagrams illustrating an embodiment ofa display device 40. The display device 40 can be, for example, acellular or mobile telephone. However, the same components of displaydevice 40 or slight variations thereof are also illustrative of varioustypes of display devices such as televisions and portable media players.

The display device 40 includes a housing 41, a display 30, an antenna43, a speaker 45, an input device 48, and a microphone 46. The housing41 is generally formed from any of a variety of manufacturing processesas are well known to those of skill in the art, including injectionmolding, and vacuum forming. In addition, the housing 41 may be madefrom any of a variety of materials, including but not limited toplastic, metal, glass, rubber, and ceramic, or a combination thereof. Inone embodiment the housing 41 includes removable portions (not shown)that may be interchanged with other removable portions of differentcolor, or containing different logos, pictures, or symbols.

The display 30 of exemplary display device 40 may be any of a variety ofdisplays, including a bi-stable display, as described herein. In otherembodiments, the display 30 includes a flat-panel display, such asplasma, EL, OLED, STN LCD, or TFT LCD as described above, or anon-flat-panel display, such as a CRT or other tube device, as is wellknown to those of skill in the art. However, for purposes of describingthe present embodiment, the display 30 includes an interferometricmodulator display, as described herein.

The components of one embodiment of exemplary display device 40 areschematically illustrated in FIG. 6B. The illustrated exemplary displaydevice 40 includes a housing 41 and can include additional components atleast partially enclosed therein. For example, in one embodiment, theexemplary display device 40 includes a network interface 27 thatincludes an antenna 43 which is coupled to a transceiver 47. Thetransceiver 47 is connected to the processor 21, which is connected toconditioning hardware 52. The conditioning hardware 52 may be configuredto condition a signal (e.g. filter a signal). The conditioning hardware52 is connected to a speaker 45 and a microphone 46. The processor 21 isalso connected to an input device 48 and a driver controller 29. Thedriver controller 29 is coupled to a frame buffer 28 and to the arraydriver 22, which in turn is coupled to a display array 30. A powersupply 50 provides power to all components as required by the particularexemplary display device 40 design.

The network interface 27 includes the antenna 43 and the transceiver 47so that the exemplary display device 40 can communicate with one oremore devices over a network. In one embodiment the network interface 27may also have some processing capabilities to relieve requirements ofthe processor 21. The antenna 43 is any antenna known to those of skillin the art for transmitting and receiving signals. In one embodiment,the antenna transmits and receives RF signals according to the IEEE802.11 standard, including IEEE 802.11(a), (b), or (g). In anotherembodiment, the antenna transmits and receives RF signals according tothe BLUETOOTH standard. In the case of a cellular telephone, the antennais designed to receive CDMA, GSM, AMPS or other known signals that areused to communicate within a wireless cell phone network. Thetransceiver 47 pre-processes the signals received from the antenna 43 sothat they may be received by and further manipulated by the processor21. The transceiver 47 also processes signals received from theprocessor 21 so that they may be transmitted from the exemplary displaydevice 40 via the antenna 43.

In an alternative embodiment, the transceiver 47 can be replaced by areceiver. In yet another alternative embodiment, network interface 27can be replaced by an image source, which can store or generate imagedata to be sent to the processor 21. For example, the image source canbe a digital video disc (DVD) or a hard-disc drive that contains imagedata, or a software module that generates image data.

Processor 21 generally controls the overall operation of the exemplarydisplay device 40. The processor 21 receives data, such as compressedimage data from the network interface 27 or an image source, andprocesses the data into raw image data or into a format that is readilyprocessed into raw image data. The processor 21 then sends the processeddata to the driver controller 29 or to frame buffer 28 for storage. Rawdata typically refers to the information that identifies the imagecharacteristics at each location within an image. For example, suchimage characteristics can include color, saturation, and gray-scalelevel.

In one embodiment, the processor 21 includes a microcontroller, CPU, orlogic unit to control operation of the exemplary display device 40.Conditioning hardware 52 generally includes amplifiers and filters fortransmitting signals to the speaker 45, and for receiving signals fromthe microphone 46. Conditioning hardware 52 may be discrete componentswithin the exemplary display device 40, or may be incorporated withinthe processor 21 or other components.

The driver controller 29 takes the raw image data generated by theprocessor 21 either directly from the processor 21 or from the framebuffer 28 and reformats the raw image data appropriately for high speedtransmission to the array driver 22. Specifically, the driver controller29 reformats the raw image data into a data flow having a raster-likeformat, such that it has a time order suitable for scanning across thedisplay array 30. Then the driver controller 29 sends the formattedinformation to the array driver 22. Although a driver controller 29,such as a LCD controller, is often associated with the system processor21 as a stand-alone Integrated Circuit (IC), such controllers may beimplemented in many ways. They may be embedded in the processor 21 ashardware, embedded in the processor 21 as software, or fully integratedin hardware with the array driver 22.

Typically, the array driver 22 receives the formatted information fromthe driver controller 29 and reformats the video data into a parallelset of waveforms that are applied many times per second to the hundredsand sometimes thousands of leads coming from the display's x-y matrix ofpixels.

In one embodiment, the driver controller 29, array driver 22, anddisplay array 30 are appropriate for any of the types of displaysdescribed herein. For example, in one embodiment, driver controller 29is a conventional display controller or a bi-stable display controller(e.g., an interferometric modulator controller). In another embodiment,array driver 22 is a conventional driver or a bi-stable display driver(e.g., an interferometric modulator display). In one embodiment, adriver controller 29 is integrated with the array driver 22. Such anembodiment is common in highly integrated systems such as cellularphones, watches, and other small area displays. In yet anotherembodiment, display array 30 is a typical display array or a bi-stabledisplay array (e.g., a display including an array of interferometricmodulators).

The input device 48 allows a user to control the operation of theexemplary display device 40. In one embodiment, input device 48 includesa keypad, such as a QWERTY keyboard or a telephone keypad, a button, aswitch, a touch-sensitive screen, a pressure- or heat-sensitivemembrane. In one embodiment, the microphone 46 is an input device forthe exemplary display device 40. When the microphone 46 is used to inputdata to the device, voice commands may be provided by a user forcontrolling operations of the exemplary display device 40.

Power supply 50 can include a variety of energy storage devices as arewell known in the art. For example, in one embodiment, power supply 50is a rechargeable battery, such as a nickel-cadmium battery or a lithiumion battery. In another embodiment, power supply 50 is a renewableenergy source, a capacitor, or a solar cell, including a plastic solarcell, and solar-cell paint. In another embodiment, power supply 50 isconfigured to receive power from a wall outlet.

In some implementations control programmability resides, as describedabove, in a driver controller which can be located in several places inthe electronic display system. In some cases control programmabilityresides in the array driver 22. Those of skill in the art will recognizethat the above-described optimization may be implemented in any numberof hardware and/or software components and in various configurations.

The details of the structure of interferometric modulators that operatein accordance with the principles set forth above may vary widely. Forexample, FIGS. 7A-7E illustrate five different embodiments of themovable reflective layer 14 and its supporting structures. FIG. 7A is across section of the embodiment of FIG. 1, where a strip of metalmaterial 14 is deposited on orthogonally extending supports 18. In FIG.7B, the moveable reflective layer 14 is attached to supports at thecorners only, on tethers 32. In FIG. 7C, the moveable reflective layer14 is suspended from a deformable layer 34, which may comprise aflexible metal. The deformable layer 34 connects, directly orindirectly, to the substrate 20 around the perimeter of the deformablelayer 34. These connections are herein referred to as support posts. Theembodiment illustrated in FIG. 7D has support post plugs 42 upon whichthe deformable layer 34 rests. The movable reflective layer 14 remainssuspended over the cavity, as in FIGS. 7A-7C, but the deformable layer34 does not form the support posts by filling holes between thedeformable layer 34 and the optical stack 16. Rather, the support postsare formed of a planarization material, which is used to form supportpost plugs 42. The embodiment illustrated in FIG. 7E is based on theembodiment shown in FIG. 7D, but may also be adapted to work with any ofthe embodiments illustrated in FIGS. 7A-7C as well as additionalembodiments not shown. In the embodiment shown in FIG. 7E, an extralayer of metal or other conductive material has been used to form a busstructure 44. This allows signal routing along the back of theinterferometric modulators, eliminating a number of electrodes that mayotherwise have had to be formed on the substrate 20.

In embodiments such as those shown in FIGS. 7A-7E, the interferometricmodulators function as direct-view devices, in which images are viewedfrom the front side of the transparent substrate 20, the side oppositeto that upon which the modulator is arranged. In these embodiments, thereflective layer 14 optically shields some portions of theinterferometric modulator on the side of the reflective layer oppositethe substrate 20, including the deformable layer 34 and the busstructure 44. This allows the shielded areas to be configured andoperated upon without negatively affecting the image quality. Thisseparable modulator architecture allows the structural design andmaterials used for the electromechanical aspects and the optical aspectsof the modulator to be selected and to function independently of eachother. Moreover, the embodiments shown in FIGS. 7C-7E have additionalbenefits deriving from the decoupling of the optical properties of thereflective layer 14 from its mechanical properties, which are carriedout by the deformable layer 34. This allows the structural design andmaterials used for the reflective layer 14 to be optimized with respectto the optical properties, and the structural design and materials usedfor the deformable layer 34 to be optimized with respect to desiredmechanical properties.

Referring to FIGS. 8 and 9, there are many mobile devices, e.g., the“clamshell” cell phone 82, that include a principle display 84 locatedon an inner surface of one half of the clamshell, and a sub-display 80located on an outer surface of the same half of clamshell as theprinciple display 84. Examples of reflective devices which can be usedas the principle display 84 and the sub-display 80 include LCD's andinterferometric modulators. In the embodiments described herein, theprinciple display 84 and/or the sub-display 80 can compriseinterferometric modulators. If the principle display 84 and thesub-display 80 are both reflective devices, they may benefit fromreceiving additional illumination when ambient light is not sufficientto view displayed information. Examples of devices for providingadditional illumination include light emitting diodes (LEDs),incandescent lamps, and fluorescent lamps. Approaches that are describedherein for providing light to the principle display 84 can also be usedto provide light to the sub-display 80, and vice-versa.

FIG. 10 shows one embodiment of a dual display 100 where a backlightlight source 90 is used to provide light to a principle display 84 and asub-display 80. In this embodiment, both the principle display 84 andthe sub-display 80 can be, e.g., LCD devices that allow light from thebacklight 90 to enter the principle display 84 and the sub-display 80through the back of the displays by using configured light leaks to theLCD devices. Providing illumination from a common backlight 90 to bothdisplays is efficient when the displays are configurable to allow lightto enter the devices from behind, e.g., through a portion of the backpanel of the display device. The displays 84 and 80 can also bereflective devices. In such embodiments, the backlight 90 may includelight leak areas or channels specifically designed to allow light topropagate directly from the backlight 90 to the front surface of thedisplays 80, 84 thereby front lighting the displays 84, 80. Otherembodiments may incorporate more than one light source to illuminate thedisplays 84, 80.

FIGS. 11 and 12 illustrate an embodiment of a dual display 100 thatincludes a backlight 90 that provides light to a principle display 84and a reflective sub-display 80 via first and second light pipes 112,114. The aperture for the light leak regions 102, 104 in a backlight canvary in size and shape. In some embodiments, the light leak region cansubstantially match the size of the area of the sub-display 80, orsubstantially match the shape of the sub-display 80, or be larger thanthe size of the perimeter of the sub-display 80, as described inreference to FIG. 13. In addition, the number of apertures or light leakregions 102, 104 disposed on the backlight 90 can vary. A light leak maybe created, for example, by removing portions of a reflective backing onthe back of a backlight to create an aperture. In certain embodiments,an optically transmissive material may be placed in the aperture of thelight leak region 102, 104. The light leak regions 102, 104 are notlimited in location to the back of the backlight, they may be located inany region of the backlight which does not interfere with the lightingor viewing of the principle display 84. For example, in someembodiments, the light leak regions 102, 104 are disposed on thebacklight 90 in the region behind the sub-display. In other embodiments,the light-leak regions may be placed on the backlight directly behindthe sub-display and/or in a region above, below or to the side or sidesof the area directly behind the sub-display (see, e.g., FIG. 11). Insome embodiments light can exit the backlight through a side surface ofthe backlight 90 (not shown), or through a portion of the surface of thebacklight 90 facing but not covered by the principle display 84.

As shown in FIG. 12, the light from the light leak regions 102, 104 canbe provided to the sub-display 80 via an optical medium such as thefirst and second light pipes 112, 114. The dual display device 100 shownin FIG. 12, comprises a backlight 90 illuminating a principle display 84that is disposed on one side of the backlight 90, and a sub-display 80disposed on the opposite side of the backlight 90. The sub-display 80shown in FIG. 12 includes a backplate 116 and is optically coupled tolight pipes 112, 114. The light leak regions 102, 104 (FIG. 11) disposedon the side of the backlight 90 facing the sub-display 80 and in an areaof the backlight not covered by the sub-display 80, can be covered bylight pipes 112, 114 (FIG. 12) so that light propagates from thebacklight 90 into the light pipes 112, 114. The light pipes 112, 114 arealso coupled to a front surface edge of the sub-display 80. In someembodiments, the light pipes 112, 114 comprise material that issubstantially optically transmissive such as, for example, polycarbonateor acrylic plastic materials. The light pipes 112, 114 can include, forexample, a solid light guide that guides the light via total internalreflection (TIR). In some embodiments, the light pipes 112, 114 includea fiber optic such as a fiber optical bundle. In certain embodiments,the light pipes 112, 114 can also be hollow, and have reflective (e.g.,metallized) surfaces to propagate light through the hollow regiontherein. Other designs of light pipes are also possible.

The light from the light source 90 can couple directly into the lightpipe 112, 114. An emitting surface of the light source 90 can bedisposed close to or possibly in contact with an input surface 111 ofthe light pipe 112, 114 to increase coupling efficiency. In theembodiment shown, the entrance 111 lies in the plane of the backlight90, corresponding to the light leak region 104 of the backlight 90. Inother embodiments, the light from the light source 90 can be coupledinto the light pipe 112, 114 through an intermediate component ormaterial.

This optically transmissive light piping 112, 114, is configured topropagate light from the backlight light source 90 to the sub-display80, to for example, a side or a portion of a side of the sub-display 80or to a surface or a portion of a surface of the sub-display 80. Thelight pipe also has an exit area 118 where light is output coupled andtransferred from the light pipe 114 to the sub-display 80.

The sub-display 80 may include an optically transmissive substrate (forexample, illustrated as substrate 20 in FIG. 1). As discussed more fullybelow in reference to FIG. 17, in some embodiments, the sub-display 80can have a frontplate (for example, optical plate 152 in FIG. 17)disposed in front of the substrate. In various embodiments, the lightpipe is optically coupled to the substrate and/or the front plate.

In the embodiment shown in FIG. 12, the exit face or aperture 118 isoriented generally perpendicular to the entrance face or aperture 111.This exit 118 may be disposed close to the edge of the frontplate and/orsubstrate of the sub-display 80. In this way, light that leaks from thebacklight 90 is output coupled into the edge of the frontplate and/orsubstrate, either or both of which may optically guide the lighttherein.

In some embodiments, a single light pipe 112 provides light to thesub-display 80. In other embodiments, two or more light pipes 112, 114provide light to the sub-display 80. In some embodiments, the light canenter the sub-display 80 at particular points. The light can be spreadacross the display 80 using various spreading or distribution techniquesas discussed more fully below. Light can be provided to the sub-display80 along one or more edges of the sub-display 80 by configuring one ormore of the light pipes 112, 114 to contact the sub-display 80 along aportion of or all of the edge of the sub-display 80.

As described above, a light pipe may be configured to couple light fromthe backlight 90 to the substrate or to a frontplate disposed forward ofthe substrate. In some embodiments, the substrate or frontplate caninclude optical features that help to re-direct light to the lightmodulating element of the sub-display 80. For example, optical featureson a surface of the substrate or a frontplate or in the substrate orfrontplate may redirect light guided through the substrate orfrontplate. In other embodiments where light is spilled onto the surfaceof the substrate or frontplate, optical features on the surface or inthe substrate or frontplate can redirect light incident on the substrateor frontplate at grazing incidence, which would otherwise not betransmitted through the frontplate or substrate, to the light modulatingelement of the display. These optical features may comprise, forexample, scatter features that scatter light or micro-optical elementsincluding but not limited to mini-prisms and micro-lenses that redirectlight. The optical features can comprise molded optics. Accordingly, theoptical features may operate on the light in a deterministic ornon-deterministic fashion. These optical features may comprise one ormore surfaces that reflect or refract light (similar, for example, tothose in a Fresnel lens or a corner turning film) to redirect the lighttoward the light modulating elements. The optical elements may besymmetric or asymmetric and may be periodic and/or non-periodic.Together the optical elements may form, for example a hologram ordiffractive optical element or a diffuser. These optical elements neednot be limited to surfaces features and may include volume features suchas in a bulk diffuser or hologram. Accordingly, the light can beredirected using reflection, refraction, diffraction, diffusion, randomor pseudo-random scattering techniques, or any combination thereof.Other configurations and approaches are also possible.

In embodiments where the light pipes 112, 114 couple light into thesubstrate, the optical couplings may provide index matching to reducereflection at the interface between the light pipe and the substrate. Incertain preferred embodiments, the exit port of the light pipes 112, 114have a numerical aperture or entendue that substantially matches thenumerical aperture or entendue of the substrate. In some embodiments,optical coupling provides a numerical aperture or entendue that matchesthat of the substrate. This optical coupling may, for example, alter thenumerical aperture or entendue of the light pipe 112, 114 tosubstantially match that of the substrate. An imaging or non-imagingoptical component may, for example, be used to achieve this conversionof numerical aperture or entendue. In some embodiments, the end of thelight pipe 112, 114 is shaped and configured to provide this conversion.

Similarly, as described below, in embodiments where the light pipes 112,114 couple light into an optical plate, sheet, layer, of thin film, theoptical couplings may provide index matching to reduce reflection.Likewise, entendue may be substantially matched to increase or maximizethroughput. In certain embodiments where the light pipes 112, 114 arecoupled to both the substrate and one or more optical plate, sheet,layer, or film thereon, entendue may be substantially matched as well toincrease throughput.

FIGS. 13A-C illustrate another embodiment of a display device 120 wherean annular light pipe 122 provides light from the backlight 90 to theedges of the sub-display 80. FIG. 13A schematically depicts a front viewof an embodiment of the annular light pipe 122 mounted on the backlight90 with the sub-display 80 inserted in the center of the annular lightpipe 122. In this configuration, light is provided by the backlight 90to all sides of the sub-display through the annular light pipe 122. FIG.13B schematically depicts a perspective view of the annular light pipeand backlight of FIG. 13A where the sub-display 80 is shown inset in theannular light pipe 122. FIG. 13C schematically depicts the annular lightpipe of FIG. 13A without the sub-display 80 and illustrates the exitports 118 of the annular light pipe.

The annular light pipe 122 has a light entrance (not shown) which couldvary in size or location. In some embodiments, the entrance of the lightpipe 122 has inner dimensions that are approximately the same shape andsize, or slightly larger or smaller, as the outline of the sub-display80. Additionally, the area of the entrance into the annular light pipe122 can correspond with the shape and size of a light-leak region on thebacklight 90. In the embodiment shown in FIGS. 13A and 13B, the annularlight pipe 122 is shaped to conform and provide light to the four edgesof the sub-display 80. The light pipe 122 is configured such that theexit portion 118 of the annular light pipe can propagate light intoportions of the edges of the sub-display 80. The size of the entrance ofthe light pipe may vary and can have a cross-sectional area that is thesame, larger or smaller than the cross-sectional area of the exit of thelight pipe. Preferably, the entrance and exit of the light pipe areconfigured so light efficiently enters the light pipe 122, propagatesthrough and exits the light pipe with reduced or minimal light loss.However, it is not required for all the light that is leaked from thebacklight 90 to exit the light pipe 122 at exit portion 118. Forexample, some light that does not initially exit the light pipe throughthe light pipe exit may be recycled back through the light pipe and intothe backlight 90. This recycled light may pass through the backlight 90to illuminate the principle display or re-enter the light pipe 122 so asto ultimately illuminate the sub-display 80. As described above, thelight pipe 122 may comprise a solid or hollow optical pipe or a fiber orfiber bundle, and other variations are also possible. The light pipe maycomprise polymer material that can be molded, for example, by injectionmolding in some embodiments. Other methods of fabricating the annularlight pipe 122 may be used. In some embodiments, the annular light pipe122 can be configured to be an attachment device that secures thesub-display 80 in the display device 120 and is optically coupled to thesub-display 80.

There are numerous alternative implementations for illuminating a dualdisplay with a single backlight. For example FIG. 14 illustratesillumination of a dual display device with the back of principle display84 facing the back of the sub-display 80, wherein the principle display84 is illuminated from a light source 191 at the edge of the principledisplay 84. The sub-display 80 is illuminated at the edge of the displayfrom the same light source 191 through a light pipe 193. The light pipe193 is optically coupled 154 to the edge of the sub-display 80 todisperse the light evenly throughout the sub-display 80. In thisembodiment, optical coupling 154 couples the light pipe 193 to thesub-display 80. The principle display 84 can be any type of display thatis configured to be illuminated on the edge of the display. In someembodiments, the sub-display 80 and/or the principle display 84 havescattering features or other optical structures disposed on or forwardof the display, for example, on a surface between the viewer and thereflective light modulating portion of the sub-display 80 or theprinciple display 84.

Additionally, the backplate of the sub-display can be used as part orall of the light pipe. In some embodiments, the light-leak from thebacklight can, for example, comprise an area defined by the area of thesub-display, e.g., essentially square or rectangular. Two examples areshown in FIGS. 15 and 16 where areas of light transfer are indicated byhatching at the light entrance 132. Referring to FIG. 15, the backplate134 of the sub-display 80 can be modified to operate as the light pipe.In some embodiments where the backplate 134 serves as a light pipe, thebackplate may have similar features to the light pipes 112, 114 andannular light pipe 122 discussed above. For example, the backplate 134may comprise optically transmissive material through which light canpropagate. The backplate 134 may, for example, comprise polymericmaterial that is molded or formed into a suitable shape, e.g., tosurround and hold the sub-display 80 and to optically couple to thelight leakage region 132. In certain embodiments, the backplate mayinclude a hollow region through which light may propagate. Additionally,the backplate may be optically coupled to the sub-display 80, or coupledto a sheet, plate, or film proximal to the display, for example, throughan optical cement.

The backplate 134 may be disposed about the display 80 to produce acavity between the display and backplate. The backplate 134 of thesub-display 80 is configured as a light pipe that receives light througha light entrance 132 and propagates the light to the front edge of thesub-display 80, where the light exits the backplate/lightpipe 134through the light exits 136, 138 and enters the sub-display 80. Similarto the light pipes 114 in FIGS. 12 and 13, the backplate 134 can beconfigured in various ways to provide light to a portion of the edge orthe entire edge of the sub-display 80.

Referring now to FIG. 16, the backplate 134 can be extended beyond theedges of the sub-display 80, and disposed such that the light exit areaof the backplate 134 is near the edge of the sub-display 80. In someembodiments, optical couplings 142, 144 can be used to optically bridgeany gap that exists between the light exit area of the backplate 134 andthe sub-display 80. The optical coupling 142, 144 can be, for example, asmall light pipe or optical coupling adhesive. The optical couplings142, 144 may include reflective surfaces therein to direct light fromthe backplate 134 into the display. In this way, the combination of thebackplate 134 and the optical couplings 142, 144 serves as the lightpipe that provides light from the backlight 90 to the sub-display 80.

FIG. 17 shows a substantially optically transmissive component 152disposed forward of the sub-display 80. In some embodiments, thesubstantially optically transmissive component is an optical plate, andin the discussion of an embodiment hereinbelow, the substantiallyoptically transmissive component will be referred to as optical plate152. In other embodiments, the substantially optically transmissivecomponent is an optical sheet, film or layer. In some embodiments, thesubstantially optically transmissive component comprises a light guide.Accordingly, the discussion provided herein with respect to the opticalplate 152 may also apply to optical sheets, films, and layers as well.

The light pipe 112, 114 may be configured to couple light from thebacklight 90 to the optical plate 152 disposed forward of thesub-display 80 (for example, between the sub-display 80 and a viewer ofthe sub-display 80). In some embodiments, the optical plate 152 caninclude optical features that help to re-direct light to the lightmodulating element of the sub-display 80. For example, optical featureson a surface of the optical plate 152 or in the optical plate 152 mayredirect light guided through the optical plate 152, e.g., by totalinternal reflection. In other embodiments where light is spilled ontothe surface of the optical plate 152, optical features on the surface orin the optical plate 152 can redirect light incident on the opticalplate 152 at or near grazing incidence. This redirected light, whichwould otherwise not be transmitted through the optical plate 152, ismade to impinge upon and illuminate the light modulating elements of thedisplay. These optical features may comprise, for example, scatterfeatures that scatter light or micro-optical elements including but notlimited to mini-prisms and micro-lenses that redirect light. The opticalfeatures can comprise molded optics. Accordingly, the optical featuresmay operate on the light in a deterministic or non-deterministicfashion. These optical features may comprise one or more surfaces thatreflect or refract light (similar, for example, to those in a Fresnellens or a corner turning film, e.g., a variation of the quarter turningfilm by 3M Corporation) to redirect the light toward the lightmodulating elements. The optical elements may be symmetric or asymmetricand may be periodic and/or non-periodic. Together the optical elementsmay form, for example a hologram or diffractive optical element or adiffuser. These optical elements need not be limited to surfacesfeatures and may include volume features such as in a bulk diffuser orhologram. Accordingly, the light can be redirected using reflection,refraction, diffraction, diffusion, random or pseudo-random scatteringtechniques, or any combination thereof. Other configurations andapproaches are also possible.

The optical plate 152 may comprise, for example, glass or plastic or anysubstantially optically transmissive (or transparent) material. In someembodiments, the optical plate 152 comprises an optical sheet, film orlayer. Such an optical sheet, film, or layer, may also comprise, e.g.,glass or polymer or other substantially optically transmissive material.In some embodiments, an optical film 152 is laminated to the substrateon which the spatial light modulator elements are formed on one or morelayers thereon. In other embodiments, the optical film 152 can be grownor may be formed in other ways, for example, optical structures may bemolded directly onto the sub-display as a permanent or removable opticalfilm.

The optical plate 152 can be optically coupled to the light pipes 112,114 by a variety of techniques. For example, optical adhesive or othercoupling material may be used as optical coupling 154, 156, or the lightpipe 112, 114 may be near or touching the optical plate 152. The opticalcoupling 154, 156 may provide index matching to reduce reflection at theinterface between the light pipes 112, 114 and the optical plate 152. Incertain preferred embodiments, the exit port of the light pipes 112, 114have a numerical aperture or entendue that substantially matches thenumerical aperture or entendue of the optical plate 152. In someembodiments, optical coupling 114, 156 provides a numerical aperture orentendue that matches that of the optical plate 152. This opticalcoupling may, for example, alter the numerical aperture or entendue ofthe light pipe to substantially match that of the optical plate 152. Animaging or a non-imaging optical component may, for example, be used toachieve this conversion of numerical aperture or entendue. In someembodiments, the ends of the light pipes 112, 114 are shaped andconfigured to provide this conversion.

The optical plate 152 may be configured to disperse the light from thelight pipes 112, 114 evenly throughout the sub-display surface. In someembodiments, the backplate 116 comprises a light pipe that couples lightinto the optical plate 152.

FIG. 18 illustrates an embodiment where the light pipes 112, 114 spillthe light 162 onto the sub-display 80 or onto an optical plate (sheet,film, or layer, etc.), such as the optical plate 152 shown in FIG. 17.The shape of the light pipe and the shape of the exit regions can betailored to distribute light in a controlled manner. In someembodiments, the sub-display 80 or optical plate 152 may be configuredto disperse the light throughout the display. Optical features may beused to re-direct light toward the light modulating elements, asdiscussed above. See, for example, discussion of FIG. 17 an associateddiscussion.

FIG. 19 illustrates an embodiment where the light pipes 112, 114 furthercomprise distal portions 164, 166 configured to control the distributionof light, e.g., distribute light 168 onto the sub-display 80 in apre-determined pattern. In some embodiments, the distal portion 164, 166of the optical pipes 112, 114 can be structured to mimic edge lightingwith LEDs. Knowledge of the pattern of the structured spill allows thesub-display 80 to be configured so as to disperse the light evenlythroughout the display with, for example, optical features in thedisplay, one or more optical plates 152 (or sheets, films, or layers) asdiscussed with reference to FIG. 17. The distal portion 164, 166 of theoptical light pipes 112, 114 can be separate components opticallycoupled to the light pipes 112, 114, or the distal portions 164, 166 maybe integrated as part of the light pipes 112, 114.

The embodiments described herein relate not only to providing light to asub-display by a dual display light source, but also to providing lightto the principle display. For example, if the principle display is areflective display that cannot receive light through its back surfacethat faces the backlight, the above-described light pipes and backplateconfigurations for the sub-display can be utilized to illuminate theprinciple display. For example, FIG. 20 illustrates a dual displayoutfitted with first and second light sources 192, 194 disposed betweenthe sub-display 80 and a principle display 182. Light pipes 181, 183,185, 187 optically couple the light sources 192, 194 to the backplates116, 117, which are also light guides. The light is further funneled byadditional optical pipes 186, 188, 196, 198 to the displays 80, 84. InFIG. 20, the additional optical pipes 186, 188, 196, 198 are opticallycoupled to an optical film or plate 174, 184 disposed forward at thedisplays 80, 84.

The optical films or plates 174, 184 may comprise optical features toredirect light toward the light modulating elements as discussed above.Also, as discussed above, the light pipes 186, 188, 196, 198 and opticalplate 152, 184 may be optically coupled in a manner that increases thetransfer of light. However, in some embodiments the additional opticalpipes 181, 183, 185, 187, 186, 188, 196, 198 and/or optical plates orfilms 174, 184 are not used, and the backplates 116, 117 are configuredto propagate the light from light sources 192, 194 either throughout thedisplays 80, 182 or to the edge of the displays which may comprisescatter features. Similarly, light may be coupled by light pipes intothe substrate in addition to or instead of the optical films or plates174, 184. A wide range of variations in configuration and designs suchas discussed above and elsewhere herein may be employed. For example,The display device of claim 30, wherein the light piping comprises asingle backplate that provides light to both the first and seconddisplays. Still other variations are possible as well.

As described above, dual display devices can include features thatre-direct (e.g., scatter) light to the reflective display. Such featuresmay comprise, for example, illumination dots, described in the commonlyowned patent application entitled “Integrated Modulator Illumination,”U.S. patent application Ser. No. 10/794,825.

An embodiment of a purely reflective display comprising a spatial lightmodulator having illumination dots is shown in FIG. 21. The spatiallight modulator in this example comprises interferometric modulatorssuch as described above used as part of the dual display device. Adiffuser 206 is disposed forward of the spatial light modulator. Theinterferometric modulator shown in FIG. 21 is formed on an opticallytransmissive substrate 200. Each element 204 of the spatial lightmodulator array can be individually activated to modulate the light thattravels through the diffuser 206 and through the substrate 200 to reachthe element 204. Each modulator element, when activated, can be used todirect modulated or non-modulated light to a viewer 214 on the oppositeside of the substrate 200. This embodiment includes a backplate 202 forthe modulator that can be opaque, rendering this type of modulatordifficult to use with backlighting. The elements 204 are themselvesopaque, which makes backlighting even more difficult.

With application of an edge lighting scheme as described herein for adual display application, illumination dots 208 formed at the interfacebetween the diffuser 206 and the substrate 200 can provide illuminationfor the display. Each dot 208 is comprised of a first layer 210 that isreflective disposed towards the modulator array and a second layer 212that is absorbing disposed towards the viewer 214. The illumination dotsmay be formed on the surface of the optically transmissive substrate 200or on the diffuser 206 (or on one or more layers formed or coupledthereon, e.g., an optical plate 152) by various types of printing orthin film deposition techniques. Other methods of forming the opticalfeatures may also be employed.

The illumination dots together with a light source associated with thedisplay can supplement ambient light, increasing the brightness of thedisplay. In total darkness, the illumination dots and the associatedlight source can provide all necessary illumination for the display.FIG. 21 shows a light source 216, such as a cold cathode fluorescenttube or a light emitting diode (LED), residing at one edge of theoptically transmissive substrate 200. An some embodiments, an edgeemitting light pipe illuminated, e.g., by a LED, may instead be employedas the light source 216. Light emitted by the light source 216 andproperly injected into the substrate 200 propagates through thesubstrate guided therein by total internal reflection. As illustrated,light striking an illumination dot is reflected in several differentdirections; see, e.g., at dots 220 and 222. As described above, in someembodiments, the light source 216 in FIG. 21 can be a light pipe thatilluminates the edge of the display, or that illuminates an opticalplate, sheet, film, or layer forward of the display.

The dots can be configured and arranged depending, for example, upon thetype and distribution of the illumination and the environment in whichthe modulator may be used as well as the design of the spatial lightmodulator. FIG. 22 shows an example of a dot pattern that is notuniform. In various embodiments, the dot arrangement may vary in manyaspects and may be, for example, irregular. The degree of regularity ofthe arrangement of dots may range from completely random, to partiallyrandom and partially regular to uniform and periodic. The arrangementmay be selected to reduce Moire effects that result from the periodicityof the light modulating elements in the modulator array or to reducefixed pattern noise. Also, as discussed above, the dots can be arrangedto distribute the light in a particular fashion, for example, evenlyacross the display for a given illumination configuration. Dots in thedot pattern, such as dot 302, deflect or scatter light whichsubsequently strikes modulator elements such as elements 304 a and 304b. The light deflected or scattered from dot 302 may have beeninternally reflected several times within substrate 200 before strikingdot 302 and being deflected or scattered.

As discussed above, light injected into the optically transmissivesubstrate 200 is internally reflected in the substrate 200. Without dotsor some other perturbing structure this light may continue to traversethe substrate 200. The dots disrupt or perturb the propagation of thelight within the substrate 200 scattering the light onto the spatiallight modulator elements 304. The dots may be arranged in a pattern toprovide for a specific distribution of light on the spatial lightmodulator array. In some embodiments, for example, the dot pattern cancreate uniform illumination on the array of spatial light modulatorelements.

In various embodiments, the dots will be of a size too small to resolveby the vision of a human observer viewing the display at a normalviewing distance. Undesirable artifacts can sometimes still be createdby arrays with features that are not individually resolvable. Thepattern can be such that these undesirable artifacts are mitigated oreliminated. As described above, the pattern can also control thedistribution of the light on the spatial light modulators.

In addition to variation in the patterning of the dots, the surface uponwhich the dots are placed may also be varied. In FIG. 23, the dots areshown at the interface between the diffuser 502 and the opticallytransmissive substrate 500. The diffuser 502 is mated to the opticallytransmissive substrate 500 in certain embodiments. For purposes of FIG.23, the diffuser has been lifted away from the substrate 500. The dotscould be patterned onto the surface of the substrate 500, such as dot504. Dot 504 has a reflective portion 508 towards the modulator array,not shown, and an absorbing portion 506 towards the viewer 214.

In an alternative embodiment, the dots can be placed on the surface ofthe diffuser 502, such as dot 510. The dots can also be formed on one ormore layers on the diffuser 502 or substrate 500 or can be formedelsewhere (e.g., on an optical plate disposed between the reflectivedisplay and a viewer of the display). Changing the position of the dotsmay modify the dot processing sequence. A dot on the surface of thesubstrate, such as 504, may have a first reflective material 508deposited and then covered by an ‘overcoat’ 506 of absorbing material.If the dots reside on the surface of the diffuser 502, such as 510, theabsorbing material 512 may be put down first, followed by the reflectivematerial 514. This approach maintains the proper orientation of thelayers with regards to the modulator and the viewer 214.

The optical features can be located elsewhere. For example, the opticalfeatures may be disposed on the surface of an optical plate (sheet,film, or layer). The optical features may also be disposed in thesubstrate or optical plate (sheet, film, or layer). Still othervariations are possible.

Although dots having a specific shape and configuration are shown inFIGS. 21-23, other types of features may be used in the substrate of thesub-display or an optical plate, sheet or film forward the sub-display.These features may, for example, comprise microstructures ormicrostructure arrays comprising, e.g., bumps, dots, or pits. Thefeatures may comprise concave or convex surfaces (e.g., that form lensesor lenlets). In some embodiments, the features are elongated andcomprise, e.g., ribs, ridges, or grooves, that may or may not bestraight. Tilted and curved surfaces may be used as well. A wide rangeof other shapes, geometries, and configurations are possible. In someembodiments, the geometries may deterministically redirect the lightinto the display. As described above, for example, micro-optics such asmicro-lenses, prisms, and corner turning films may be used. The featuresmay, for example, redirect light disposed at any angle on the surface ofthe display to fold into the display for proper illumination.Non-deterministic approaches may be employed. The optical features maycomprise features that form a diffuser, a diffractive optical element,or a hologram.

These features may have regular or irregular shape and may havedifferent dimensions. The features may comprise opaque or substantiallyoptically transmissive material. The features may be partially orcompletely reflective, transmissive, and/or absorbing. The features maycomprise metal in some embodiments or may comprise dielectric. Thefeatures may comprise dielectric having an index of refraction that isthe same or different than the surface (e.g., substrate, diffuser,optical plate, other layers etc.) on which the features are formed. Somemicrostructure arrays can have dimensions on the order of microns.

The features can be fabricated in different ways as well. The featurescan be applied, for example, by printing or lithographically, byinjection molding or laser etching. The features can be applied onto asurface as a film. In an alternative embodiment, light scattering and/ordirecting microstructures can be manufactured and bonded onto a surfaceof the display, optical film or plate using resin which is molded andcured to form a desired microstructure, for example usingultraviolet-setting resin. Other methods of fabricating the scatteringfeatures are also possible.

In addition to the flexibility in forming the optical features on avariety of surfaces of the display and the flexibility as to whatpattern and density the optical features are formed, there is alsoconsiderable flexibility as to the point in a manufacturing process atwhich the optical feature are created. Some exemplary methods formanufacturing spatial light modulator arrays with illumination dots areshown in FIG. 24.

In one embodiment, the process starts with providing a substantiallyoptically transmissive substrate at block 600. The illumination dots areapplied to the optically transmissive substrate or any optical plate,sheet or film 152 forward of the display at block 602. The spatial lightmodulator is manufactured at block 604. The modulator is finished atblock 606, which may include such tasks as attaching a backplate. Thediffuser is applied to the substrate or any optical plate 152, forwardthe display, over the illumination dots, at block 608. Other componentsmay also be included.

In an alternative embodiment, the spatial light modulator ismanufactured on the ‘back side’ (away from the viewer) of thesubstantially optically transmissive substrate at block 610. The spatiallight modulator is finished at block 612. In one embodiment, theillumination dots are applied to the front side of the substrate atblock 614 and the diffuser is applied at block 616.

In another alternative, a diffuser is supplied at block 618 either afterthe modulator is finished at block 612 or in parallel with the processof manufacturing and finishing the modulator. The illumination dots areapplied to the diffuser at block 620 and the diffuser is applied to thesubstrate at block 622.

Other methods may also be used. No order is implied by the listing theprocesses, as the order may change depending upon the embodiment.Additionally, processing steps may be added or removed.

As described above, the optical features may be formed in one of manyprinting procedures, including, e.g., lithographic printing, inkjetprinting, screen-printing or any other type of printing technique.Non-printing based methods may also be used. The optical features can,for example, be embossed onto the surface or molded. The opticalfeatures may be formed on a surface that is laminated or adhered to thesubstrate or optical plate or other layer. Still other techniques,including both those well known in the art as well as those yet to bedevised may be employed. The shape and configurations of the opticalfeatures may be controlled to increase or maximize effectiveness. Asmentioned above, the optical features can be fabricated at a resolutionbelow the resolution of the human eye to avoid affecting the imagequality as seen by the viewer.

While the above detailed description has shown, described, and pointedout novel features of the invention as applied to various embodiments,it will be understood that various omissions, substitutions, and changesin the form and details of the device or process illustrated may be madeby those skilled in the art without departing from the spirit of theinvention. As will be recognized, the present invention may be embodiedwithin a form that does not provide all of the features and benefits setforth herein, as some features may be used or practiced separately fromothers.

1-47. (canceled)
 48. A display device comprising: a first display, saidfirst display being reflective; a light source disposed rearward of saidfirst display; one or more first light guides disposed to receive lightfrom said light source; and one or more second light guides disposedforward of said first display, wherein the one or more first lightguides are optically coupled to the one or more second light guides suchthat light emitted by the one or more first light guides is directedinto said one or more second light guides, to provide front illuminationto said first display
 49. The display of claim 48, further comprising asecond display positioned such that said light source is disposedrearward of said second display, wherein said light source providesillumination to said second display.
 50. The display of claim 48,wherein said one or more first light guides comprises a backplatedisposed rearward of said first display.
 51. The display of claim 48,wherein said one or more second light guides comprises an optical plate,sheet, or film.
 52. The display of claim 48, wherein said one or moresecond light guides comprises a substrate of the first display.
 53. Thedisplay of claim 48, wherein said first display comprises a plurality oflight modulating elements.
 54. The display of claim 53, wherein saidplurality of light modulating elements comprises a plurality ofinterferometric modulators.
 55. The display of claim 48, wherein saidone or more second light guides includes optical features configured toredirect said light coupled therein to said first display.
 56. Thedisplay of claim 55, wherein said optical features include mini-prisms,micro-lenses, a hologram, a diffractive optical element, or a diffuser.57. The display device of claim 48, further comprising: a processor inelectrical communication with said first display, said processorconfigured to process image data; and a memory device in electricalcommunication with said processor.
 58. The display device of claim 57,further comprising a driver circuit configured to send at least onesignal to said first display.
 59. The display system of claim 58,further comprising a controller configured to send at least a portion ofsaid image data to said driver circuit.
 60. A method of manufacturing adisplay device, the method comprising: providing a first display, saidfirst display being reflective; providing a light source disposedrearward of said first display; providing one or more first light guidesdisposed to receive light from said light source; and providing a secondlight guide forward of said first display, such that the one or morefirst light guides are optically coupled to the second light guide suchthat light emitted by the one or more first light guides is directedinto said second light guide, to provide front illumination to saidfirst display.
 61. The method of claim 60, further comprising providinga second display such that said light source is disposed rearward ofsaid second display, wherein said light source provides illumination tosaid second display.
 62. The method of claim 60, wherein said one ormore first light guides comprises a backplate disposed rearward of saidfirst displaying means.
 63. The method of claim 60, wherein said secondlight guide comprises an optical plate, sheet, or film.
 64. The methodof claim 60, wherein said second light guide comprises a substrate ofthe first display.
 65. The method of claim 60, wherein said firstdisplay comprises a plurality of light modulating elements.
 66. Themethod of claim 65, wherein said plurality of light modulating elementscomprises a plurality of interferometric modulators.
 67. The method ofclaim 60, wherein said second light guide includes optical featuresconfigured to redirect said light coupled therein to said first display.68. The method of claim 67, wherein said optical features includemini-prisms, micro-lenses, a hologram, a diffractive optical element, ora diffuser.